You cannot become licensed (they do not certify) in Zumba online. They do have a big list of instructor training sites; perhaps one will come to your area in the future. http://www.zumba.com/en-US/trainings/basic1
In the meantime I would recommend becoming certified as a group fitness instructor so you have a good knowledge base to teach classes. Zumba does not teach that.
If there are no trainings in your area, you can consider being a host facility. We have regular B1 trainings at a nearby location, but I’ve hosted Zumba Toning, Zumba Gold (3 times), and am about to host Zumba Step. If you’re in a well-populated area you might just get a training nearby. If you’re not in a well-populated area, you might have to consider traveling to get your license.
I agree with Janet’s suggestion to get a group-ex certification in addition.